Flow control in subterranean wells

ABSTRACT

A method of restoring flow through an opening in a well, the opening being blocked by a plugging device, can include conveying a well tool into the well, contacting the plugging device with the well tool, and permitting flow through the opening as a result of the contacting step. Another method of restoring flow through an opening blocked by a plugging device in a well can include conveying a well tool into the well, reducing pressure in the well with the well tool, and permitting flow through the opening as a result of the pressure reducing step.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 15/567,779which is: 1) a national stage under 35 USC 371 of InternationalApplication No. PCT/US16/29314, filed on 26 Apr. 2016, 2) acontinuation-in-part of each of U.S. application Ser. No. 14/698,578filed 28 Apr. 2015 and International application serial no.PCT/US15/38248 filed 29 Jun. 2015, and 3) claims the benefit of thefiling date of U.S. provisional application Ser. No. 62/252,174 filed 6Nov. 2015. The entire disclosures of these prior applications areincorporated herein in their entireties by this reference.

BACKGROUND

This disclosure relates generally to equipment utilized and operationsperformed in conjunction with a subterranean well and, in one exampledescribed below, more particularly provides for flow control in wells.

It can be beneficial to be able to control how and where fluid flows ina well. For example, it may be desirable in some circumstances to beable to prevent fluid from flowing into a particular formation zone. Asanother example, it may be desirable in some circumstances to causefluid to flow into a particular formation zone, instead of into anotherformation zone. Therefore, it will be readily appreciated thatimprovements are continually needed in the art of controlling fluid flowin wells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representative partially cross-sectional view of an exampleof a well system and associated method which can embody principles ofthis disclosure.

FIGS. 2A-D are enlarged scale representative partially cross-sectionalviews of steps in an example of a re-completion method that may bepracticed with the system of FIG. 1.

FIGS. 3A-D are representative partially cross-sectional views of stepsin another example of a method that may be practiced with the system ofFIG. 1.

FIGS. 4A & B are enlarged scale representative elevational views ofexamples of a flow conveyed device that may be used in the system andmethods of FIGS. 1-3D, and which can embody the principles of thisdisclosure.

FIG. 5 is a representative elevational view of another example of theflow conveyed device.

FIGS. 6A & B are representative partially cross-sectional views of theflow conveyed device in a well, the device being conveyed by flow inFIG. 6A, and engaging a casing opening in FIG. 6B.

FIGS. 7-9 are representative elevational views of examples of the flowconveyed device with a retainer.

FIG. 10 is a representative partially cross-sectional view of an exampleof a technique for removing the flow conveyed plugging device from anopening.

FIG. 11 is a representative partially cross-sectional view of anotherexample of a technique for removing the flow conveyed plugging devicefrom an opening.

FIGS. 12 & 13 are representative cross-sectional views of additionalexamples of the flow conveyed device.

FIG. 14 is a representative cross-sectional view of a well tool that maybe operated using the flow conveyed device.

DETAILED DESCRIPTION

Representatively illustrated in FIG. 1 is a system 10 for use with awell, and an associated method, which can embody principles of thisdisclosure. However, it should be clearly understood that the system 10and method are merely one example of an application of the principles ofthis disclosure in practice, and a wide variety of other examples arepossible. Therefore, the scope of this disclosure is not limited at allto the details of the system 10 and method described herein and/ordepicted in the drawings.

In the FIG. 1 example, a tubular string 12 is conveyed into a wellbore14 lined with casing 16 and cement 18. Although multiple casing stringswould typically be used in actual practice, for clarity of illustrationonly one casing string 16 is depicted in the drawings.

Although the wellbore 14 is illustrated as being vertical, sections ofthe wellbore could instead be horizontal or otherwise inclined relativeto vertical. Although the wellbore 14 is completely cased and cementedas depicted in FIG. 1, any sections of the wellbore in which operationsdescribed in more detail below are performed could be uncased or openhole. Thus, the scope of this disclosure is not limited to anyparticular details of the system 10 and method.

The tubular string 12 of FIG. 1 comprises coiled tubing 20 and a bottomhole assembly 22. As used herein, the term “coiled tubing” refers to asubstantially continuous tubing that is stored on a spool or reel 24.The reel 24 could be mounted, for example, on a skid, a trailer, afloating vessel, a vehicle, etc., for transport to a wellsite. Althoughnot shown in FIG. 1, a control room or cab would typically be providedwith instrumentation, computers, controllers, recorders, etc., forcontrolling equipment such as an injector 26 and a blowout preventerstack 28.

As used herein, the term “bottom hole assembly” refers to an assemblyconnected at a distal end of a tubular string in a well. It is notnecessary for a bottom hole assembly to be positioned or used at a“bottom” of a hole or well.

When the tubular string 12 is positioned in the wellbore 14, an annulus30 is formed radially between them. Fluid, slurries, etc., can be flowedfrom surface into the annulus 30 via, for example, a casing valve 32.One or more pumps 34 may be used for this purpose. Fluid can also beflowed to surface from the wellbore 14 via the annulus 30 and valve 32.

Fluid, slurries, etc., can also be flowed from surface into the wellbore14 via the tubing 20, for example, using one or more pumps 36. Fluid canalso be flowed to surface from the wellbore 14 via the tubing 20.

In the further description below of the examples of FIGS. 2A-9, one ormore flow conveyed devices are used to block or plug openings in thesystem 10 of FIG. 1. However, it should be clearly understood that thesemethods and the flow conveyed device may be used with other systems, andthe flow conveyed device may be used in other methods in keeping withthe principles of this disclosure.

The example methods described below allow existing fluid passageways tobe blocked permanently or temporarily in a variety of differentapplications. Certain flow conveyed device examples described below aremade of a fibrous material and comprise a central body, a “knot” orother enlarged geometry. Other flow control device examples may not bemade of a fibrous material, may not have a centrally positioned body,and/or may not comprise a knot.

The devices are conveyed into leak paths using pumped fluid. Fibrousmaterial extending outwardly from a body of a device can “find” andfollow the fluid flow, pulling the enlarged geometry into a restrictedportion of a flow path, causing the enlarged geometry and additionalstrands to become tightly wedged into the flow path thereby sealing offfluid communication.

The devices can be made of degradable or non-degradable materials. Thedegradable materials can be either self-degrading, or can requiredegrading treatments, such as, by exposing the materials to certainacids, certain base compositions, certain chemicals, certain types ofradiation (e.g., electromagnetic or “nuclear”), or elevated temperature.The exposure can be performed at a desired time using a form of wellintervention, such as, by spotting or circulating a fluid in the well sothat the material is exposed to the fluid.

In some examples, the material can be an acid degradable material (e.g.,nylon, etc.), a mix of acid degradable material (for example, nylonfibers mixed with particulate such as calcium carbonate), self-degradingmaterial (e.g., poly-lactic acid (PLA), poly-glycolic acid (PGA), etc.),material that degrades by galvanic action (such as, magnesium alloys,aluminum alloys, etc.), a combination of different self-degradingmaterials, or a combination of self-degrading and non-self-degradingmaterials.

Multiple materials can be pumped together or separately. For example,nylon and calcium carbonate could be pumped as a mixture, or the nyloncould be pumped first to initiate a seal, followed by calcium carbonateto enhance the seal.

In certain examples described below, the device can be made of knottedfibrous materials. Multiple knots can be used with any number of looseends. The ends can be frayed or un-frayed. The fibrous material can berope, fabric, cloth or another woven or braided structure.

The device can be used to block open sleeve valves, perforations or anyleak paths in a well (such as, leaking connections in casing, corrosionholes, etc.). An opening in a well tool, whether formed intentionally orinadvertently, can be blocked using the device. Any opening throughwhich fluid flows can be blocked with a suitably configured device.

In one example method described below, a well with an existingperforated zone can be re-completed. Devices (either degradable ornon-degradable) are conveyed by flow to plug all existing perforations.

The well can then be re-completed using any desired completiontechnique. If the devices are degradable, a degrading treatment can thenbe placed in the well to open up the plugged perforations (if desired).

In another example method described below, multiple formation zones canbe perforated and fractured (or otherwise stimulated, such as, byacidizing) in a single trip of the bottom hole assembly 22 into thewell. In the method, one zone is perforated, the zone is fractured orotherwise stimulated, and then the perforated zone is plugged using oneor more devices.

These steps are repeated for each additional zone, except that a lastzone may not be plugged. All of the plugged zones are eventuallyunplugged by waiting a certain period of time (if the devices areself-degrading), by applying an appropriate degrading treatment, or bymechanically removing the devices.

Referring specifically now to FIGS. 2A-D, steps in an example of amethod in which the bottom hole assembly 22 of FIG. 1 can be used inre-completing a well are representatively illustrated. In this method(see FIG. 2A), the well has existing perforations 38 that provide forfluid communication between an earth formation zone 40 and an interiorof the casing 16. However, it is desired to re-complete the zone 40, inorder to enhance the fluid communication.

Referring additionally now to FIG. 2B, the perforations 38 are plugged,thereby preventing flow through the perforations into the zone 40. Plugs42 in the perforations can be flow conveyed devices, as described morefully below. In that case, the plugs 42 can be conveyed through thecasing 16 and into engagement with the perforations 38 by fluid flow 44.

Referring additionally now to FIG. 2C, new perforations 46 are formedthrough the casing 16 and cement 18 by use of an abrasive jet perforator48. In this example, the bottom hole assembly 22 includes the perforator48 and a circulating valve assembly 50. Although the new perforations 46are depicted as being formed above the existing perforations 38, the newperforations could be formed in any location in keeping with theprinciples of this disclosure.

Note that other means of providing perforations 46 may be used in otherexamples. Explosive perforators, drills, etc., may be used if desired.The scope of this disclosure is not limited to any particularperforating means, or to use with perforating at all.

The circulating valve assembly 50 controls flow between the coiledtubing 20 and the perforator 48, and controls flow between the annulus30 and an interior of the tubular string 12. Instead of conveying theplugs 42 into the well via flow 44 through the interior of the casing 16(see FIG. 2B), in other examples the plugs could be deployed into thetubular string 12 and conveyed by fluid flow 52 through the tubularstring prior to the perforating operation. In that case, a valve 54 ofthe circulating valve assembly 50 could be opened to allow the plugs 42to exit the tubular string 12 and flow into the interior of the casing16 external to the tubular string.

Referring additionally now to FIG. 2D, the zone 40 has been fractured orotherwise stimulated by applying increased pressure to the zone afterthe perforating operation. Enhanced fluid communication is now permittedbetween the zone 40 and the interior of the casing 16.

Note that fracturing is not necessary in keeping with the principles ofthis disclosure. Although certain examples described herein utilizefracturing, it should be understood that other types of stimulationoperations (such as acidizing) may be performed instead of, or inaddition to, fracturing.

In the FIG. 2D example, the plugs 42 prevent the pressure applied tofracture the zone 40 via the perforations 46 from leaking into the zonevia the perforations 38. The plugs 42 may remain in the perforations 38and continue to prevent flow through the perforations, or the plugs maydegrade, if desired, so that flow is eventually permitted through theperforations.

In other examples, fractures may be formed via the existing perforations38, and no new perforations may be formed. In one technique, pressuremay be applied in the casing 16 (e.g., using the pump 34), therebyinitially fracturing the zone 40 via some of the perforations 38 thatreceive most of the fluid flow 44. After the initial fracturing of thezone 40, and while the fluid is flowed through the casing 16, plugs 42can be released into the casing, so that the plugs seal off thoseperforations 38 that are receiving most of the fluid flow.

In this way, the fluid 44 will be diverted to other perforations 38, sothat the zone 40 will also be fractured via those other perforations 38.The plugs 42 can be released into the casing 16 continuously orperiodically as the fracturing operation progresses, so that the plugsgradually seal off all, or most, of the perforations 38 as the zone 40is fractured via the perforations. That is, at each point in thefracturing operation, the plugs 42 will seal off those perforations 38through which most of the fluid flow 44 passes, which are theperforations via which the zone 40 has been fractured.

Referring additionally now to FIGS. 3A-D, steps in another example of amethod in which the bottom hole assembly 22 of FIG. 1 can be used incompleting multiple zones 40 a-c of a well are representativelyillustrated. The multiple zones 40 a-c are each perforated and fracturedduring a single trip of the tubular string 12 into the well.

In FIG. 3A, the tubular string 12 has been deployed into the casing 16,and has been positioned so that the perforator 48 is at the first zone40 a to be completed. The perforator 48 is then used to formperforations 46 a through the casing 16 and cement 18, and into the zone40 a.

In FIG. 3B, the zone 40 a has been fractured by applying increasedpressure to the zone via the perforations 46 a. The fracturing pressuremay be applied, for example, via the annulus 30 from the surface (e.g.,using the pump 34 of FIG. 1), or via the tubular string 12 (e.g., usingthe pump 36 of FIG. 1). The scope of this disclosure is not limited toany particular fracturing means or technique, or to the use offracturing at all.

After fracturing of the zone 40 a, the perforations 46 a are plugged bydeploying plugs 42 a into the well and conveying them by fluid flow intosealing engagement with the perforations. The plugs 42 a may be conveyedby flow 44 through the casing 16 (e.g., as in FIG. 2B), or by flow 52through the tubular string 12 (e.g., as in FIG. 2C).

The tubular string 12 is repositioned in the casing 16, so that theperforator 48 is now located at the next zone 40 b to be completed. Theperforator 48 is then used to form perforations 46 b through the casing16 and cement 18, and into the zone 40 b. The tubular string 12 may berepositioned before or after the plugs 42 a are deployed into the well.

In FIG. 3C, the zone 40 b has been fractured by applying increasedpressure to the zone via the perforations 46 b. The fracturing pressuremay be applied, for example, via the annulus 30 from the surface (e.g.,using the pump 34 of FIG. 1), or via the tubular string 12 (e.g., usingthe pump 36 of FIG. 1).

After fracturing of the zone 40 b, the perforations 46 b are plugged bydeploying plugs 42 b into the well and conveying them by fluid flow intosealing engagement with the perforations. The plugs 42 b may be conveyedby flow 44 through the casing 16, or by flow 52 through the tubularstring 12.

The tubular string 12 is repositioned in the casing 16, so that theperforator 48 is now located at the next zone 40 c to be completed. Theperforator 48 is then used to form perforations 46 c through the casing16 and cement 18, and into the zone 40 c. The tubular string 12 may berepositioned before or after the plugs 42 b are deployed into the well.

In FIG. 3D, the zone 40 c has been fractured by applying increasedpressure to the zone via the perforations 46 c. The fracturing pressuremay be applied, for example, via the annulus 30 from the surface (e.g.,using the pump 34 of FIG. 1), or via the tubular string 12 (e.g., usingthe pump 36 of FIG. 1).

In some examples, the perforations 46 c could be plugged after the zone40 c is fractured or otherwise stimulated. For example, such plugging ofthe perforations 46 c could be performed in order to verify that theplugs are effectively blocking flow from the casing 16 to the zones 40a-c.

The plugs 42 a,b are then degraded and no longer prevent flow throughthe perforations 46 a,b. Thus, as depicted in FIG. 3D, flow is permittedbetween the interior of the casing 16 and each of the zones 40 a-c.

The plugs 42 a,b may be degraded in any manner. The plugs 42 a,b maydegrade in response to application of a degrading treatment, in responseto passage of a certain period of time, or in response to exposure toelevated downhole temperature. The degrading treatment could includeexposing the plugs 42 a,b to a particular type of radiation, such aselectromagnetic radiation (e.g., light having a certain wavelength orrange of wavelengths, gamma rays, etc.) or “nuclear” particles (e.g.,gamma, beta, alpha or neutron).

The plugs 42 a,b may degrade by galvanic action or by dissolving. Theplugs 42 a,b may degrade in response to exposure to a particular fluid,either naturally occurring in the well (such as water or hydrocarbonfluid), or introduced therein (such as a fluid having a particular pH).

Note that any number of zones may be completed in any order in keepingwith the principles of this disclosure. The zones 40 a-c may be sectionsof a single earth formation, or they may be sections of separateformations.

In other examples, the plugs 42 may not be degraded. The plugs 42 couldinstead be mechanically removed, for example, by milling or otherwisecutting the plugs 42 away from the perforations, or by grabbing andpulling the plugs from the perforations. In any of the method examplesdescribed above, after the fracturing or other stimulating operation(s)are completed, the plugs 42 can be milled off or otherwise removed fromthe perforations 38, 46, 46 a,b without dissolving, melting, dispersingor otherwise degrading a material of the plugs.

Referring additionally now to FIG. 4A, an example of a flow conveyeddevice 60 that can incorporate the principles of this disclosure isrepresentatively illustrated. The device 60 may be used for any of theplugs 42, 42 a,b in the method examples described above, or the devicemay be used in other methods.

The device 60 example of FIG. 4A includes multiple fibers 62 extendingoutwardly from an enlarged body 64. As depicted in FIG. 4A, each of thefibers 62 has a lateral dimension (e.g., a thickness or diameter) thatis substantially smaller than a size (e.g., a thickness or diameter) ofthe body 64.

The body 64 can be dimensioned so that it will effectively engage andseal off a particular opening in a well. For example, if it is desiredfor the device 60 to seal off a perforation in a well, the body 64 canbe formed so that it is somewhat larger than a diameter of theperforation. If it is desired for multiple devices 60 to seal offmultiple openings having a variety of dimensions (such as holes causedby corrosion of the casing 16), then the bodies 64 of the devices can beformed with a corresponding variety of sizes.

In the FIG. 4A example, the fibers 62 are joined together (e.g., bybraiding, weaving, cabling, etc.) to form lines 66 that extend outwardlyfrom the body 64. In this example, there are two such lines 66, but anynumber of lines (including one) may be used in other examples.

The lines 66 may be in the form of one or more ropes, in which case thefibers 62 could comprise frayed ends of the rope(s). In addition, thebody 64 could be formed by one or more knots in the rope(s). In someexamples, the body 64 can comprise a fabric or cloth, the body could beformed by one or more knots in the fabric or cloth, and the fibers 62could extend from the fabric or cloth.

In the FIG. 4A example, the body 64 is formed by a double overhand knotin a rope, and ends of the rope are frayed, so that the fibers 62 aresplayed outward. In this manner, the fibers 62 will cause significantfluid drag when the device 60 is deployed into a flow stream, so thatthe device will be effectively “carried” by, and “follow,” the flow.

However, it should be clearly understood that other types of bodies andother types of fibers may be used in other examples. The body 64 couldhave other shapes, the body could be hollow or solid, and the body couldbe made up of one or multiple materials. The fibers 62 are notnecessarily joined by lines 66, and the fibers are not necessarilyformed by fraying ends of ropes or other lines. Thus, the scope of thisdisclosure is not limited to the construction, configuration or otherdetails of the device 60 as described herein or depicted in thedrawings.

Referring additionally now to FIG. 4B, another example of the device 60is representatively illustrated. In this example, the device 60 isformed using multiple braided lines 66 of the type known as “masontwine.” The multiple lines 66 are knotted (such as, with a double ortriple overhand knot or other type of knot) to form the body 64. Ends ofthe lines 66 are not necessarily frayed in these examples, although thelines do comprise fibers (such as the fibers 62 described above).

Referring additionally now to FIG. 5, another example of the device 60is representatively illustrated. In this example, four sets of thefibers 62 are joined by a corresponding number of lines 66 to the body64. The body 64 is formed by one or more knots in the lines 66.

FIG. 5 demonstrates that a variety of different configurations arepossible for the device 60. Accordingly, the principles of thisdisclosure can be incorporated into other configurations notspecifically described herein or depicted in the drawings. Such otherconfigurations may include fibers joined to bodies without use of lines,bodies formed by techniques other than knotting, etc.

Referring additionally now to FIGS. 6A & B, an example of a use of thedevice 60 of FIG. 4 to seal off an opening 68 in a well isrepresentatively illustrated. In this example, the opening 68 is aperforation formed through a sidewall 70 of a tubular string 72 (suchas, a casing, liner, tubing, etc.). However, in other examples theopening 68 could be another type of opening, and may be formed inanother type of structure.

The device 60 is deployed into the tubular string 72 and is conveyedthrough the tubular string by fluid flow 74. The fibers 62 of the device60 enhance fluid drag on the device, so that the device is influenced todisplace with the flow 74.

Since the flow 74 (or a portion thereof) exits the tubular string 72 viathe opening 68, the device 60 will be influenced by the fluid drag toalso exit the tubular string via the opening 68. As depicted in FIG. 6B,one set of the fibers 62 first enters the opening 68, and the body 64follows. However, the body 64 is appropriately dimensioned, so that itdoes not pass through the opening 68, but instead is lodged or wedgedinto the opening. In some examples, the body 64 may be received onlypartially in the opening 68, and in other examples the body may beentirely received in the opening.

The body 64 may completely or only partially block the flow 74 throughthe opening 68. If the body 64 only partially blocks the flow 74, anyremaining fibers 62 exposed to the flow in the tubular string 72 can becarried by that flow into any gaps between the body and the opening 68,so that a combination of the body and the fibers completely blocks flowthrough the opening.

In another example, the device 60 may partially block flow through theopening 68, and another material (such as, calcium carbonate, PLA or PGAparticles) may be deployed and conveyed by the flow 74 into any gapsbetween the device and the opening, so that a combination of the deviceand the material completely blocks flow through the opening.

The device 60 may permanently prevent flow through the opening 68, orthe device may degrade to eventually permit flow through the opening. Ifthe device 60 degrades, it may be self-degrading, or it may be degradedin response to any of a variety of different stimuli. Any technique ormeans for degrading the device 60 (and any other material used inconjunction with the device to block flow through the opening 68) may beused in keeping with the scope of this disclosure.

In other examples, the device 60 may be mechanically removed from theopening 68. For example, if the body 64 only partially enters theopening 68, a mill or other cutting device may be used to cut the bodyfrom the opening.

Referring additionally now to FIGS. 7-9, additional examples of thedevice 60 are representatively illustrated. In these examples, thedevice 60 is surrounded by, encapsulated in, molded in, or otherwiseretained by, a retainer 80.

The retainer 80 aids in deployment of the device 60, particularly insituations where multiple devices are to be deployed simultaneously. Insuch situations, the retainer 80 for each device 60 prevents the fibers62 and/or lines 66 from becoming entangled with the fibers and/or linesof other devices.

The retainer 80 could in some examples completely enclose the device 60.In other examples, the retainer 80 could be in the form of a binder thatholds the fibers 62 and/or lines 66 together, so that they do not becomeentangled with those of other devices.

In some examples, the retainer 80 could have a cavity therein, with thedevice 60 (or only the fibers 62 and/or lines 66) being contained in thecavity. In other examples, the retainer 80 could be molded about thedevice 60 (or only the fibers 62 and/or lines 66).

At least after deployment of the device 60 into the well, the retainer80 dissolves, melts, disperses or otherwise degrades, so that the deviceis capable of sealing off an opening 68 in the well, as described above.For example, the retainer 80 can be made of a material 82 that degradesin a wellbore environment.

The retainer material 82 may degrade after deployment into the well, butbefore arrival of the device 60 at the opening 68 to be plugged. Inother examples, the retainer material 82 may degrade at or after arrivalof the device 60 at the opening 68 to be plugged. If the device 60 alsocomprises a degradable material, then preferably the retainer material82 degrades prior to the device material.

The material 82 could, in some examples, melt at elevated wellboretemperatures. The material 82 could be chosen to have a melting pointthat is between a temperature at the earth's surface and a temperatureat the opening 68, so that the material melts during transport from thesurface to the downhole location of the opening.

The material 82 could, in some examples, dissolve when exposed towellbore fluid. The material 82 could be chosen so that the materialbegins dissolving as soon as it is deployed into the wellbore 14 andcontacts a certain fluid (such as, water, brine, hydrocarbon fluid,etc.) therein. In other examples, the fluid that initiates dissolving ofthe material 82 could have a certain pH range that causes the materialto dissolve.

Note that it is not necessary for the material 82 to melt or dissolve inthe well. Various other stimuli (such as, passage of time, elevatedpressure, flow, turbulence, etc.) could cause the material 82 todisperse, degrade or otherwise cease to retain the device 60. Thematerial 82 could degrade in response to any one, or a combination, of:passage of a predetermined period of time in the well, exposure to apredetermined temperature in the well, exposure to a predetermined fluidin the well, exposure to radiation in the well and exposure to apredetermined chemical composition in the well. Thus, the scope of thisdisclosure is not limited to any particular stimulus or technique fordispersing or degrading the material 82, or to any particular type ofmaterial.

In some examples, the material 82 can remain on the device 60, at leastpartially, when the device engages the opening 68. For example, thematerial 82 could continue to cover the body 64 (at least partially)when the body engages and seals off the opening 68. In such examples,the material 82 could advantageously comprise a relatively soft, viscousand/or resilient material, so that sealing between the device 60 and theopening 68 is enhanced.

Suitable relatively low melting point substances that may be used forthe material 82 can include wax (e.g., paraffin wax, vegetable wax),ethylene-vinyl acetate copolymer (e.g., ELVAX™ available from DuPont),atactic polypropylene and eutectic alloys. Suitable relatively softsubstances that may be used for the material 82 can include a softsilicone composition or a viscous liquid or gel. Suitable dissolvablematerials can include PLA, PGA, anhydrous boron compounds (such asanhydrous boric oxide and anhydrous sodium borate), polyvinyl alcohol(PVA), polyvinyl acetate (PVAc), polyethylene oxide, salts andcarbonates.

In FIG. 7, the retainer 80 is in a cylindrical form. The device 60 isencapsulated in, or molded in, the retainer material 82. The fibers 62and lines 66 are, thus, prevented from becoming entwined with the fibersand lines of any other devices 60.

In FIG. 8, the retainer 80 is in a spherical form. In addition, thedevice 60 is compacted, and its compacted shape is retained by theretainer material 82. A shape of the retainer 80 can be chosen asappropriate for a particular device 60 shape, in compacted orun-compacted form. A frangible coating 88 may be provided on theretainer 80.

In FIG. 9, the retainer 80 is in a cubic form. Thus, any type of shape(polyhedron, spherical, cylindrical, etc.) may be used for the retainer80, in keeping with the principles of this disclosure.

In some examples, the devices 60 can be prepared from non-fibrous ornonwoven material, and the devices may or may not be knotted. Thedevices 60 can also be prepared from film, tube, or nonwoven fabric. Thedevices 60 may be prepared from a single sheet of material or multiplestrips of sheet material.

Polyvinyl alcohol (PVA) and polyvinyl acetate (PVAc) are described aboveas suitable soluble retainer materials 82, but these materials may beused for the device 60 itself (with or without the retainer 80). PVA isavailable with dissolution temperatures in water over a wide range(e.g., ambient temperature to 175° F.). PVA and PVAc can be used in theform of film, tube, and fiber or filament.

Some advantages of PVA include: 1) PVA can be formulated to be insolubleat a typically lowered circulating temperature during a fracturingoperation, and later dissolve when heated to bottom hole statictemperature. No additional treatment is required to remove the knot orother plugging device made with PVA. 2) PVA can be cross-linked withborate ion or aluminum ion to decrease its dissolution rate. 3) PVAproperties can be modified by varying a degree of hydrolysis,copolymerization, or addition of plasticizer.

An example of a PVA knot device 60 can be formed as follows: A length ofPVA tube (for example, a 4 inch (˜10 cm) width flat tube made from 3 mil(˜0.08 mm) M1030 PVA film available from MonoSol, LLC of Portage, Ind.USA) is turned halfway inside-out to form a double-walled tube. The tubeis folded in half lengthwise and one end is pinched in a vise. The otherend is connected to a vacuum pump to remove air from the tube. Theresulting flattened tube is twisted into a tight strand. The resultingstrand is tied in a triple overhand knot. The knot can be seated againsta 0.42 inch (˜10.7 mm) diameter orifice and pressurized to 4500 psi (˜31MPa) with water. The knot seals the orifice, completely shutting off theflow of water.

Another material suitable for use in the device 60 is an acid-resistantmaterial that is water-soluble. Poly-methacrylic acid is insoluble atlow pH, but dissolves at neutral pH. Devices 60 made frompoly-methacrylic acid could be used as a diverter in an acid treatmentto block treated perforations and divert the acid to other perforations.After the treatment is complete, the devices 60 would dissolve as the pHrises. No remedial treatment would be required to remove the plugs.

Referring additionally now to FIG. 10, a method 100 of restoring flowthrough the openings 68 in the well is representatively illustrated. Theopenings 68 in this example are formed by perforations 46 through casing16 and cement 18 lining the wellbore 14, and flow through the openingshas previously been blocked by flow conveyed plugging devices 60 (forexample, as part of a stimulation operation).

In other examples, the openings 68 may not be formed by perforationsthrough casing or liner. The openings 68 could be formed in a side orend of a well tool, could be formed in a casing or liner withoutperforating, etc. The scope of this disclosure is not limited to anyparticular type of opening blocked by the plugging device 60.

In the FIG. 10 example, when it is desired to restore fluidcommunication between the interior of the casing 16 and the formation 40penetrated by the perforations 46, a well tool 102 is conveyed into thewellbore 14. The well tool 102 in this example has cutters 104 at adistal end thereof.

The well tool 102 may be of the type known to those skilled in the artas a mill, an overshot or a fishing tool. However, it should be clearlyunderstood that the scope of this disclosure is not limited to use ofany particular type of well tool for restoring flow through the openings68.

It is not necessary for the well tool 102 to include the cutters 104 asdepicted in FIG. 10. In some examples, the well tool 102 could beconfigured to dislodge the plugging devices 60, without cutting into theplugging devices, or without use of the cutters 104. For example, agauge of the type used to verify an inner diameter of casing could beused to contact and dislodge the plugging devices 60 from the openings68.

In the FIG. 10 example, the well tool 102 is conveyed through the casing16, so that the cutters 104 contact and cut into the plugging devices60. If the plugging devices 60 comprise a material degradable inresponse to contact with a fluid in the well, the degradable materialcan be exposed to the fluid as a result of the well tool 102 cuttinginto the plugging devices (for example, the degradable material could becoated or covered by a non-degradable material that is penetrated by thecutters 104). When the material degrades, flow through the openings 68will be restored.

In some examples, the cutters 104 could comprise one or more fluid jetnozzles. Fluid can be pumped out of the nozzles, so that fluid jets willcontact and/or cut into the plugging devices 60, in order to dislodgethe plugging devices from the openings 68 or to expose a degradablematerial of the plugging devices to fluid in the well (e.g., the fluiddischarged from the nozzles, or fluid already present in the wellbore14).

In some examples, the cutters 104 could serve to engage or “grab” theplugging devices 60, and pull the plugging devices from the openings 68.When the plugging devices 60 are dislodged from the openings 68, flowthrough the openings is restored.

Referring additionally now to FIG. 11, another example of the method 100is representatively illustrated. In this example, the well tool 102includes seals 106 that can sealingly engage the interior of the casing16. The seals 106 may be of the type known to those skilled in the artas “swab cups.”

In the FIG. 11 example, the well tool 102 is lowered through thewellbore 14, until it is relatively close to the plugging devices 60 andopenings 68. The well tool 102 is then relatively quickly displacedupward, to thereby produce a reduced pressure in the wellbore 14proximate the plugging devices 60 and openings 68.

Preferably, the pressure in the wellbore 14 becomes less than pressurein the formation 40, so that a pressure differential is created acrossthe plugging devices 60. This pressure differential biases the pluggingdevices 60 inward, so that they are dislodged from the openings 68. Whenthe plugging devices are dislodged, flow through the openings 68 isrestored.

Pressure in the well can be reduced by use of techniques other thandisplacement of the well tool 102. For example, a relatively lowpressure chamber could be opened in the well proximate the pluggingdevices 60 and openings 68 to thereby allow well fluid to enter thechamber and reduce pressure in the well. Thus, the scope of thisdisclosure is not limited to any particular technique for reducingpressure in the well.

Note that the method 100 examples as depicted in FIGS. 10 & 11 aremerely a few of a wide variety of different techniques that can be usedto restore flow through openings in a well. In some examples, flowthrough openings may be restored by the plugging devices degrading orbecoming dislodged from the openings without use of the well tool 102 orany other intervention into the well. Therefore, the scope of thisdisclosure is not limited to use of the well tool 102 or any otherintervention into the well.

Referring additionally now to FIG. 12, a cross-sectional view of anotherexample of the device 60 is representatively illustrated. The device 60may be used in any of the systems and methods described herein, or maybe used in other systems and methods.

In this example, the body of the device 60 is made up of filaments orfibers 62 formed in the shape of a ball or sphere. Of course, othershapes may be used, if desired.

The filaments or fibers 62 may make up all, or substantially all, of thedevice 60. The fibers 62 may be randomly oriented, or they may bearranged in various orientations as desired.

In the FIG. 12 example, the fibers 62 are retained by the dissolvable,degradable or dispersible material 82. In addition, a frangible coatingmay be provided on the device 60, for example, in order to delaydissolving of the material 82 until the device has been deployed into awell (as in the examples of FIGS. 8 & 10).

The device 60 of FIG. 12 can be used in a diversion fracturing operation(in which perforations receiving the most fluid are plugged to divertfluid flow to other perforations), in a re-completion operation (e.g.,as in the FIGS. 2A-D example), or in a multiple zone perforate andfracture operation (e.g., as in the FIGS. 3A-D example).

One advantage of the FIG. 12 device 60 is that it is capable of sealingon irregularly shaped openings, perforations, leak paths or otherpassageways. The device 60 can also tend to “stick” or adhere to anopening, for example, due to engagement between the fibers 62 andstructure surrounding (and in) the opening. In addition, there is anability to selectively seal openings.

The fibers 62 could, in some examples, comprise wool fibers. The device60 may be reinforced (e.g., using the material 82 or another material)or may be made entirely of fibrous material with a substantial portionof the fibers 62 randomly oriented.

The fibers 62 could, in some examples, comprise metal wool, or crumpledand/or compressed wire. Wool may be retained with wax or other material(such as the material 82) to form a ball, sphere, cylinder or othershape.

In the FIG. 12 example, the material 82 can comprise a wax (or eutecticmetal or other material) that melts at a selected predeterminedtemperature. A wax device 60 may be reinforced with fibers 62, so thatthe fibers and the wax (material 82) act together to block a perforationor other passageway.

The selected melting point can be slightly below a static wellboretemperature. The wellbore temperature during fracturing is typicallydepressed due to relatively low temperature fluids entering wellbore.After fracturing, wellbore temperature will typically increase, therebymelting the wax and releasing the reinforcement fibers 62.

This type of device 60 in the shape of a ball or other shapes may beused to operate downhole tools in a similar fashion. In FIG. 14, a welltool 110 is depicted with a passageway 112 extending longitudinallythrough the well tool. The well tool 110 could, for example, beconnected in the casing 16 of FIG. 1, or it could be connected inanother tubular string (such as a production tubing string, the tubularstring 12, etc.).

The device 60 is depicted in FIG. 14 as being sealingly engaged with aseat 114 formed in a sliding sleeve 116 of the well tool 110. When thedevice 60 is so engaged in the well tool 110 (for example, after thewell tool is deployed into a well and appropriately positioned), apressure differential may be produced across the device and the slidingsleeve 116, in order to shear frangible members 118 and displace thesleeve downward (as viewed in FIG. 14), thereby allowing flow betweenthe passageway 112 and an exterior of the well tool 110 via openings 120formed through an outer housing 122.

The material 82 of the device 60 can then dissolve, disperse orotherwise degrade to thereby permit flow through the passageway 112. Ofcourse, other types of well tools (such as, packer setting tools, fracplugs, testing tools, etc.) may be operated or actuated using the device60 in keeping with the scope of this disclosure.

A drag coefficient of the device 60 in any of the examples describedherein may be modified appropriately to produce a desired result. Forexample, in a diversion fracturing operation, it is typically desirableto block perforations in a certain location in a wellbore. The locationis usually at the perforations taking the most fluid.

Natural fractures in an earth formation penetrated by the wellbore makeit so that certain perforations receive a larger portion of fracturingfluids. For these situations and others, the device 60 shape, size,density and other characteristics can be selected, so that the devicetends to be conveyed by flow to a certain corresponding section of thewellbore.

For example, devices 60 with a larger coefficient of drag (Cd) may tendto seat more toward a toe of a generally horizontal or lateral wellbore.Devices 60 with a smaller Cd may tend to seat more toward a heel of thewellbore. For example, if the wellbore 14 depicted in FIG. 2B ishorizontal or highly deviated, the heel would be at an upper end of theillustrated wellbore, and the toe would be at the lower end of theillustrated wellbore (e.g., the direction of the fluid flow 44 is fromthe heel to the toe).

Smaller devices 60 with long fibers 62 floating freely (see the exampleof FIG. 13) may have a strong tendency to seat at or near the heel. Adiameter of the device 60 and the free fiber 62 length can beappropriately selected, so that the device is more suited to stoppingand sealingly engaging perforations anywhere along the length of thewellbore.

Acid treating operations can benefit from use of the device 60 examplesdescribed herein. Pumping friction causes hydraulic pressure at the heelto be considerably higher than at the toe. This means that the fluidvolume pumped into a formation at the heel will be considerably higherthan at the toe. Turbulent fluid flow increases this effect. Gellingadditives might reduce an onset of turbulence and decrease the magnitudeof the pressure drop along the length of the wellbore.

Higher initial pressure at the heel allows zones to be acidized and thenplugged starting at the heel, and then progressively down along thewellbore. This mitigates waste of acid from attempting to acidize all ofthe zones at the same time.

The free fibers 62 of the FIGS. 4-6B & 13 examples greatly increase theability of the device 60 to engage the first open perforation (or otherleak path) it encounters. Thus, the devices 60 with low Cd and longfibers 62 can be used to plug from upper perforations to lowerperforations, while turbulent acid with high frictional pressure drop isused so that the acid treats the unplugged perforations nearest the topof the wellbore with acid first.

In examples of the device 60 where a wax material (such as the material82) is used, the fibers 62 (including the body 64, lines 66, knots,etc.) may be treated with a treatment fluid that repels wax (e.g.,during a molding process). This may be useful for releasing the wax fromthe fibrous material after fracturing or otherwise compromising theretainer 80 and/or a frangible coating thereon.

Suitable release agents are water-wetting surfactants (e.g., alkyl ethersulfates, high hydrophilic-lipophilic balance (HLB) nonionicsurfactants, betaines, alkyarylsulfonates, alkyldiphenyl ethersulfonates, alkyl sulfates). The release fluid may also comprise abinder to maintain the knot or body 64 in a shape suitable for molding.One example of a binder is a polyvinyl acetate emulsion.

Broken-up or fractured devices 60 can have lower Cd. Broken-up orfractured devices 60 can have smaller cross-sections and can passthrough the annulus 30 between tubing 20 and casing 16 more readily.

The restriction 98 (see FIG. 10) may be connected in any line or pipethat the devices 60 are pumped through, in order to cause the devices tofracture as they pass through the restriction. This may be used to breakup and separate devices 60 into wax and non-wax parts. The restriction98 may also be used for rupturing a frangible coating covering a solublewax material 82 to allow water or other well fluids to dissolve the wax.

Fibers 62 may extend outwardly from the device 60, whether or not thebody 64 or other main structure of the device also comprises fibers. Forexample, a ball (or other shape) made of any material could have fibers62 attached to and extending outwardly therefrom. Such a device 60 willbe better able to find and cling to openings, holes, perforations orother leak paths near the heel of the wellbore, as compared to the ball(or other shape) without the fibers 62.

For any of the device 60 examples described herein, the fibers 62 maynot dissolve, disperse or otherwise degrade in the well. In suchsituations, the devices 60 (or at least the fibers 62) may be removedfrom the well by swabbing, scraping, circulating, milling or othermechanical methods.

In situations where it is desired for the fibers 62 to dissolve,disperse or otherwise degrade in the well, nylon is a suitable acidsoluble material for the fibers. Nylon 6 and nylon 66 are acid solubleand suitable for use in the device 60. At relatively low welltemperatures, nylon 6 may be preferred over nylon 66, because nylon 6dissolves faster or more readily.

Self-degrading fiber devices 60 can be prepared from poly-lactic acid(PLA), poly-glycolic acid (PGA), or a combination of PLA and PGA fibers62. Such fibers 62 may be used in any of the device 60 examplesdescribed herein.

Fibers 62 can be continuous monofilament or multifilament, or choppedfiber. Chopped fibers 62 can be carded and twisted into yarn that can beused to prepare fibrous flow conveyed devices 60.

The PLA and/or PGA fibers 62 may be coated with a protective material,such as calcium stearate, to slow its reaction with water and therebydelay degradation of the device 60. Different combinations of PLA andPGA materials may be used to achieve corresponding different degradationtimes or other characteristics.

PLA resin can be spun into fiber of 1-15 denier, for example. Smallerdiameter fibers 62 will degrade faster. Fiber denier of less than 5 maybe most desirable. PLA resin is commercially available with a range ofmelting points (e.g., 140 to 365° F.). Fibers 62 spun from lower meltingpoint PLA resin can degrade faster.

PLA bi-component fiber has a core of high-melting point PLA resin and asheath of low-melting point PLA resin (e.g., 140° F. melting pointsheath on a 265° F. melting point core). The low-melting point resin canhydrolyze more rapidly and generate acid that will acceleratedegradation of the high-melting point core. This may enable thepreparation of a fibrous device 60 that will have higher strength in awellbore environment, yet still degrade in a reasonable time. In variousexamples, a melting point of the resin can decrease in a radiallyoutward direction in the fiber.

It may now be fully appreciated that the above disclosure providessignificant advancements to the art of controlling flow in subterraneanwells. In some examples described above, the device 60 may be used toblock flow through openings in a well, with the device being uniquelyconfigured so that its conveyance with the flow is enhanced.

The above disclosure provides to the art a method 100 of restoring flowthrough an opening 68 in a well, the opening being blocked by a pluggingdevice 60. In one example, the method 100 comprises conveying a welltool 102 into the well, contacting the plugging device 60 with the welltool 102, and permitting flow through the opening 68 as a result of thecontacting step.

The plugging device 60 may include a body 64 that prevents flow throughthe opening 68 prior to the contacting step. The body 64 may comprise aknot. The body 64 may comprise a degradable material.

The plugging device 60 may also include, extending outwardly from thebody 64, at least one of fibers 62 and lines 66. The at least one offibers 62 and lines 66 may extend through the opening 68 prior to thecontacting step. The at least one of fibers 62 and lines 66 may extendinto a perforation 46 prior to the contacting step.

The plugging device 60 may include, extending outwardly from the body64, at least one of film, tube, filament, fabric and sheet material. Theat least one of film, tube, filament, fabric and sheet material mayextend through the opening 68 prior to the contacting step. The at leastone of film, tube, filament, fabric and sheet material may extend into aperforation 68 prior to the contacting step.

The contacting step may include cutting into the plugging device 60. Thecutting step may include exposing a degradable material of the pluggingdevice 60 to fluid in the well. The degradable material may be selectedfrom the group consisting of poly-vinyl alcohol, poly-vinyl acetate andpoly-methacrylic acid.

The contacting step may include engaging the plugging device 60 anddislodging the plugging device from the opening 68. The contacting stepmay include contacting the plugging device 60 with a fluid jet.

Another method 100 of restoring flow through an opening 68 blocked by aplugging device 60 in a well is provided to the art by the abovedisclosure. In one example, the method 100 can comprise conveying a welltool 102 into the well, reducing pressure in the well with the well tool102, and permitting flow through the opening 68 as a result of thepressure reducing step.

The plugging device 60 may include a body 64 that prevents flow throughthe opening 68 prior to the pressure reducing step. The body 64 maycomprise a knot.

The body 64 may comprise a degradable material. The degradable materialmay be selected from the group consisting of poly-vinyl alcohol,poly-vinyl acetate and poly-methacrylic acid.

The plugging device 60 can include, extending outwardly from the body64, at least one of the group consisting of fibers 62 and lines 66. Theat least one of fibers 62 and lines 66 may extend through the opening 68prior to the pressure reducing step.

The plugging device 60 can include, extending outwardly from the body64, at least one of film, tube, filament, fabric and sheet material. Theat least one of film, tube, filament, fabric and sheet material mayextend through the opening 68 prior to the pressure reducing step.

The pressure reducing step may comprise creating a pressure differentialacross the plugging device 60. The pressure differential creating stepmay comprise biasing the plugging device 60 inward.

The pressure reducing step can include dislodging the plugging device 60from the opening 68. The pressure reducing step can include displacingseals 106 in the well.

Although various examples have been described above, with each examplehaving certain features, it should be understood that it is notnecessary for a particular feature of one example to be used exclusivelywith that example. Instead, any of the features described above and/ordepicted in the drawings can be combined with any of the examples, inaddition to or in substitution for any of the other features of thoseexamples. One example's features are not mutually exclusive to anotherexample's features. Instead, the scope of this disclosure encompassesany combination of any of the features.

Although each example described above includes a certain combination offeatures, it should be understood that it is not necessary for allfeatures of an example to be used. Instead, any of the featuresdescribed above can be used, without any other particular feature orfeatures also being used.

It should be understood that the various embodiments described hereinmay be utilized in various orientations, such as inclined, inverted,horizontal, vertical, etc., and in various configurations, withoutdeparting from the principles of this disclosure. The embodiments aredescribed merely as examples of useful applications of the principles ofthe disclosure, which is not limited to any specific details of theseembodiments.

In the above description of the representative examples, directionalterms (such as “above,” “below,” “upper,” “lower,” etc.) are used forconvenience in referring to the accompanying drawings. However, itshould be clearly understood that the scope of this disclosure is notlimited to any particular directions described herein.

The terms “including,” “includes,” “comprising,” “comprises,” andsimilar terms are used in a non-limiting sense in this specification.For example, if a system, method, apparatus, device, etc., is describedas “including” a certain feature or element, the system, method,apparatus, device, etc., can include that feature or element, and canalso include other features or elements. Similarly, the term “comprises”is considered to mean “comprises, but is not limited to.”

Of course, a person skilled in the art would, upon a carefulconsideration of the above description of representative embodiments ofthe disclosure, readily appreciate that many modifications, additions,substitutions, deletions, and other changes may be made to the specificembodiments, and such changes are contemplated by the principles of thisdisclosure. For example, structures disclosed as being separately formedcan, in other examples, be integrally formed and vice versa.Accordingly, the foregoing detailed description is to be clearlyunderstood as being given by way of illustration and example only, thespirit and scope of the invention being limited solely by the appendedclaims and their equivalents.

What is claimed is:
 1. A method of restoring flow through an openingblocked by a plugging device in a well, the method comprising: conveyinga well tool into the well; reducing pressure in the well with the welltool; and permitting flow through the opening as a result of thepressure reducing, wherein the plugging device comprises a body thatprevents flow through the opening prior to the pressure reducing, thebody comprises a knot, and the knot engages but is too large to passthrough the opening.
 2. The method of claim 1, wherein the bodycomprises a degradable material.
 3. The method of claim 2, wherein thedegradable material is selected from the group consisting of poly-vinylalcohol, poly-vinyl acetate, poly-methacrylic acid, poly-lactic acid andpoly-glycolic acid.
 4. The method of claim 1, wherein the pluggingdevice further comprises, extending outwardly from the body, at leastone of the group consisting of fibers and lines.
 5. The method of claim4, wherein the at least one of the group consisting of fibers and linesextends through the opening prior to the pressure reducing.
 6. Themethod of claim 1, wherein the plugging device further comprises,extending outwardly from the body, at least one of the group consistingof film, tube, filament, fabric and sheet material.
 7. The method ofclaim 6, wherein the at least one of the group consisting of film, tube,filament, fabric and sheet material extends through the opening prior tothe pressure reducing.
 8. The method of claim 1, wherein the pressurereducing comprises creating a pressure differential across the pluggingdevice.
 9. The method of claim 8, wherein the pressure differentialcreating comprises biasing the plugging device inward.
 10. The method ofclaim 1, wherein the pressure reducing comprises dislodging the pluggingdevice from the opening.
 11. The method of claim 1, wherein the pressurereducing comprises displacing seals in the well.